Relativistic hydro and magnetohydrodynamic models for AGN jet propagation and deceleration

Abstract

We present grid-adaptive computational studies of both magnetized and unmagnetized jet flows, with significantly relativistic bulk speeds, as appropriate for AGN jets. Our relativistic jet studies shed light on the observationally established classification of Fanaroff-Riley galaxies, where the appearance in radio maps distinguishes two types of jet morphologies. The computational effort involves modern shock-capturing schemes exploited at very high effective resolutions due to the dynamic grid adaptivity. Our parallel MPI-AMRVAC code allows for direct comparisons between TVD Lax-Friedrichs, HLL, HLLC, and approximate Riemann solver based schemes for hydro and magnetohydrodynamic applications, in both classical and relativistic variants. We investigate how density changes in the external medium can induce one-sided jet decelerations, explaining the existence of hybrid morphology radio sources. Our simulations explore under which conditions highly energetic FR II jets may suddenly decelerate and continue with FR I characteristics. Apart from this externally induced effect, we study intrinsic jet properties that shed light on FR I/II behavior. For the latter, we explore the consequences of a radially structured jet morphology, where interface dynamics can trigger transitions to highly turbulent flow regimes. Finally, we explore the role of dynamically important, organized magnetic fields in the collimation of the relativistic jet flows. We show that the helicity of the magnetic field is effectively transported down the beam, with compression zones in between diagonal internal cross-shocks showing stronger toroidal field regions. The axial flow can reaccelerate downstream to these internal cross-shocks, as field compression pinches the flow.